Maintenance and development of taste buds depend on neurotrophic influences, but it is not entirely clear which nerve fibers, gustatory or general sensory, are responsible for stimulating epithelial morphodifferentiation. It is also unclear what role each fiber type may play in the formation of the gustatory pathway and in maturation of the taste organ. Although the anatomical and functional aspects of the gustatory system have been well described in adult mammals and amphibians, relatively little is known about its development. The study of neurodevelopment is difficult in mammals because of the complexity of their nervous systems and inaccessibility of the embryos. To circumvent these difficulties, the comparatively simple and more accessible peripheral nervous system of Xenopus laevis will be used in the proposed study to provide an account of developing peripheral taste pathways. The growth of taste and somatosensory fibers toward targets in the oral epithelium will be examined, including the correlation with developing taste organs. The earliest stages of axonal migration will be identified using HNK-1 antibody which has been shown to label a transient cell surface molecule on developing neurons in Xenopus and other vertebrates. It is proposed that HNK-1 can be used successfully to label developing peripheral axons. Developing taste pathways will be mapped using successively older animals. A detailed account will be made of the precise distribution of outgrowing processes, the nature of their environment, and relationship to other neighboring axons and developing taste buds. The specific aims of this proposal are: 1. To evaluate Xenopus laevis as a model system for studying the developing gustatory system. 2. To test the effectiveness of HNK-1 antibody for labeling peripheral taste axons. This proposal will provide information in two areas. First, examination of developing gustatory pathways will begin to answer one of the basic questions of neurobiology: How are the pathways of the peripheral nervous system initially laid out? Second, the study will provide basic information for those who are developing strategies to examine the loss of taste acuity due to trauma, disease, irradiation, drugs, or aging. An understanding of the relationship between a neuron and its target is essential for grasping the most basic concepts of growth and regeneration.